Earth's core

REUTERS photo

A woman and her daughter touch a structural model of the earth's core at Nanjing Geological Museum in Nanjing, Jiangsu province. Earth Day, which is celebrated on April 22 every year, marks an annual effort to raise public awareness about the environment and inspire actions to clean it up. The Chinese characters on the model read "outer core."

A woman and her daughter touch a structural model of the earth's core at Nanjing Geological Museum in Nanjing, Jiangsu province. Earth Day, which is celebrated on April 22 every year, marks an annual effort to raise public awareness about the environment and inspire actions to clean it up. The Chinese characters on the model read "outer core." (REUTERS photo)

A woman and her daughter touch a structural model of the earth's core at Nanjing Geological Museum in Nanjing, Jiangsu province. Earth Day, which is celebrated on April 22 every year, marks an annual effort to raise public awareness about the environment and inspire actions to clean it up. The Chinese characters on the model read "outer core."